Prior Art
Prior art cited in this application:
U.S. PatentsPat. No.Issue DatePatentee8,813,4742014 Aug. 26Daniau, et al.5,921,7651999 Jul. 13Smith5,797,2601998 Aug. 25Koppel5,361,5811994 Nov. 8Clark4,722,1851988 Feb. 2Campbell3,163,0011964 Dec. 29Reilly3,088,4061963 May 7Horner2,920,4441960 Jan. 12Jorgensen2,512,2541950 Jun. 20Mallory2,480,5401949 Aug. 30Bodine1,035,4541912 Aug. 13Lewis
The pulse jet engine is one of the simplest, and easiest to manufacture thrust generating devices. It is also a device fraught with problems. The pulse jet is inefficient, has poor thrust to size ratio, generally poor thrust characteristics which severely limit speed or applicable force, and limited options for improving compression and overall burn. U.S. Pat. No. 2,480,540, 1949, A. G. Bodine, Jr. attempts to overcome these limits by using a piston, or comparable pressure reacting device, to transfer combustion pressure to a compressor. This engine still operates on resonance, would still need a long resonance tube, and the added compression would blow a fair amount of fuel air mixture out of the appropriate combustion zone because of poor contain. Plus, the added complexity negates the simple nature of a pulse jet engine.
U.S. Pat. No. 8,813,474, 2014, E. Daniau, et al, claims a pulse detonation engine. The more immediate combustion of pulse detonation is an effort to make up for the lack of contain and compression present in a typical pulse jet engine. However the Daniau design still operates on a cycle, still necessarily employs a long fire tube, and the movable unit positioned at the combustion point is specifically designed to regulate fuel.
Other efforts work to forgo the long resonance tube of the pulse jet, while improving compression and contain. Typically, but not always, a crankshaft driven reciprocating piston compressor is used. The next five designs are indicative of this approach. But, whatever differences these designs have with regard to each other, they all need to manage the compressed air. Combustion drives the compression stage. But, combustion also occupies the combustion chamber the compressed air needs to fill. So, some way is needed to manage the gas until the chamber clears. Also, compressors need to cycle, complicating coordination of events.
A shortcoming in U.S. Pat. No. 3,163,001, 1964, J. Reilly design is a dual piston approach to defining the combustion chamber. No matter the variant, these two pistons need a mechanism to coordinate their movements. The built in delay chamber also underscores the need for compressed air management.
In U.S. Pat. No. 2,920,444, 1960, W. Jorgensen, which uses a linear reciprocating piston, the air fuel mixture is fed into an open combustion chamber. This design ultimately fires when the combustion chamber is closed. But, filling the combustion chamber with the air fuel mixture this way can lead to a number of problems, depending on the actual timing of events. The air fuel mixture can leak out the exhaust port, leaving less than the ideal maximum in the combustion chamber. The mixture can be pushed out, at least in part, by the return of the piston to its closed position. Also, the unit could misfire if fuel and air are introduced into the chamber while burn is still occurring.
U.S. Pat. No. 5,361,581, 1994, B. Clark shows a typical approach to a reciprocating pulse jet engine. The additional drawback here is the piston provides a larger workable surface to the forces of combustion than does the exhaust port. This means work preferentially goes to the piston, and so, to the full crankshaft rotation, not out as thrust. This has been a major stumbling block for all designs like this.
U.S. Pat. No. 1,035,454, 1912, I. Lewis is an earlier version of a high compression pulse jet design. It uses a two tiered piston to present a smaller workable surface to the combustion chamber. However, when the two tiered piston pulls out of the combustion chamber, the large compression piston places a draw on the combustion chamber, possibly compromising thrust and drawing in combustion product, contaminating the next charge.
In the U.S. Pat. No. 2,512,254, 1950, M. Mallory a distinct valve is used to separate the thrust combustion chamber from the compressor combustion chamber. This calls for a distinct mechanism to operate this valve. The open thrust chamber variant would be plagued with burn propagation and contain issues.
The preceding examples all operate on some form of cycle. These cycles make it difficult for these designs to have single fire or intermittent operation. Also, these designs are intricately tied to their compressors. This can have severe limitations on their form factors and design applications.
Some rocket engine designs operate on a metered out burn principle which may resemble an impulse style thrust burst. Three such units, U.S. Pat. No. 3,088,406, 1963, J. Horner, U.S. Pat. No. 4,722,185, 1988, R. Campbell, and U.S. Pat. No. 5,797,260, 1998, C. Koppel, L. Maine, all employ pistons in some form. Aside from the open combustion chamber and special fuel requirements, all three designs simply use the pistons to meter out the necessary fuel mixture for burn. Even the Koppel design, which places a piston in the combustion chamber, uses thrust to push the piston into a set fuel mixture volume to squeeze the fuel into the combustion chamber. This may produce a thrust event closer to an impulse thrust event, but these devices are clearly operationally different and would have limits typical of rockets.
U.S. Pat. No. 5,921,765, 1999, by B. Smith is a combustion management device. Aside from being attached to a specific compressed fuel/oxidizer source, the Smith design has another notable difference. The Smith design has a piston acting as an exhaust valve that is pushed by the expanding gases to release the combusted gas stream. This push open valve design does nothing to recover the work applied to it in a manner that compliments the thrust vector created. And, it would be extremely difficult, if not impossible, to modify the physical geometry and mechanisms of the Smith design to accomplish this. Also, optimizing the Smith design combustion chamber to expel the combusted products effectively and efficiently would be difficult, if not impractical.